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Thread: COG.....PLEASE read!

  1. #1
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    COG.....PLEASE read!

    Maybe we can stop claiming we all know everything about COG, since the damn thing changes all the time. If we all knew everything about it, we may be standing and walking. If you want to argue, argue with Tilite.
    http://www.tilite.com/assets/pdf/RIGID_OM_TR_YR.pdf

    Emjoy! This is printed in your owners manual. I would be willing to bet everything I own, NOBODY has ever read it, including me.

  2. #2
    Senior Member jschism's Avatar
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    my upper body acts like a pendulum and is always perfectly vertical over the pivot point of my center of mass when sitting in my chair, therefore my COG never changes.

  3. #3
    Senior Member DaleB's Avatar
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    COG...please give it a rest!

    I read every post that goes by in the Equipment forum and I don't recall anyone claiming to know it all. However, some people certainly do know more than others when it comes to seating, stability, and mating clinical needs with functional goals. End users and manufactures can have good data points, but considering the source, one by definition limited and the other out for money, I know who I go to first for my seating issues: professional, degreed & certified, experienced seating OTs. Finding one that is also a user is even better.

    In the context of medical necessity all opinions aren't created equal.
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  4. #4
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    Obviously TiLite places warnings like this as a disclaimer, against complaints and lawsuits. If you really consider, able bodied people deal with COG with every active thing they do. Those of us who can remember being AB probably don't remember because it is somewhat instinctive.

    Since we first learned to crawl and then walk we have had to deal with our changing center of gravity. This behavior may be mostly learned but at some point it does become automatic for us. Now that we are in wheelchairs, we have to relearn how to do this. Nice of TiLite to remind us of this.
    Last edited by ala; 10-12-2012 at 10:21 AM. Reason: one wrong word

  5. #5
    I really don't see how this is supposed to rebut anything that anyone has posted regarding COG. All of the things listed in that section are a given. While it may not be the case the majority of the time, these are things everyone should understand before they are discharged from rehab.

    In the past, my main "arguments" with TiLite were related to the narrow fork they used a couple of years ago which prevented users from being able to use a 1.5" wide soft roll caster and their previous practice of charging an additional $150 to get a 1" longer frame. Both of those issues were directly related to the management of stability. Both of those issues have been remedied.

    My concept of "Dynamic Wheeled Mobility" challenges the notion that the configuration of a wheelchair has to be something static--where the performance of the chair is determined by the lowest common denominator. For example, consider Brian's post in another thread...

    Quote Originally Posted by brian View Post
    For those of you with a very-forward COG, how do you get up hills?
    My COG is as far back as I can set it just so I can tackle steep driveways, grassy knolls, and cities like SF and Seattle.
    Should someone have to live with a configuration set up to be able to get up hills on occasion and have to settle for a front heavy chair the rest of the time? Does it have to be that way? Not necessarily. That's where the concept of Dynamic Wheeled Mobility comes in. There are a number of ways to accomplish this.

    Products like the Firefly, SmartDrive, ZX1, and Freewheel represent the "add on" approach to overcoming limitations of the user's primary ultralight configuration.

    Specific features designed into the chair, such as user adjustable back angles, (Ki Mobility's Rogue, Quickie's GT/Q7, Elevation, Marvel, and the Icon A-1) represent an "integrated" approach where a feature's design provides some ability to dynamically change the configuration to match the demands of the environment.

    I believe that even more is possible with creative engineering if designer's made the concept more of a priority during the design phase and actual end users started thinking about their chairs and what they would like to be able to do while using them. Would Bill Lasher, Jr. have developed the BT-X if he wasn't a para?

    http://lashersport.com/products-BT-X.html
    Last edited by SCI_OTR; 10-13-2012 at 11:47 AM. Reason: Expounded More


  6. #6
    Senior Member grommet's Avatar
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    That is interesting as hell! I'm picturing traveling through an airport, with luggage through a hotel. I wonder. I don't expext I'll own a Lasher but they're awfully nice looking seem very strong. As it is I am getting great performance from my Tilite but that trailer looks pretty cool.

    http://lashersport.com/products-BT-X.html

  7. #7
    IMO the same holds true for pressure measurement. Many, if not most, people simply do a static measure of cushion efficacy with the user sitting in place. However, really good techs/professionals do a dynamic test with the user wheeling around. My tech has a pressure pad attached to a laptop enabling the person to wheel around. It gives a picture of what happens when weight is shifted during wheeling and other activity. Certainly sitting is in place is most important but shear and other forces should be considered.
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  8. #8

  9. #9
    Quote Originally Posted by rlmtrhmiles View Post
    More relevant for wheelchair users.

    http://ptjournal.apta.org/content/80/9/904.full

    Highly technical and unlikely to be totally understood the first time through.

    It also incorporates the concept of rolling resistance. Rolling resistance is a very important concept. Most chairs would never flip going up a ramp if it were not for rolling resistance. Most of the time it is the force from the user's propulsion, that causes the chair to flip back. If rolling resistance exceeds that force, the chair cannot roll forward and those forces are redirected elsewhere.

    Another classic example is the inexperinced user who flips their chair trying to get over a 1" threshold because they were at a dead stop and tried using brute force to roll over it. They could not overcome rolling resistance. A mini-wheelie, on the other hand, reduces rolling resistance.


  10. #10
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    sci....I understand all you are saying. It really is a "relative" number based on all the data assesed at that exact time. I think it would be better for vendors to describe it someho w as "balance" and not COG. The earth spins. It moves around the sun. Technically that can factor in. Your 2nd paragraph from bottom describes the "uh oh!" I am on the floor ans smashed my head. You understand what we are talking here.

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